Large thick-walled plastic containers are used for packaging and transporting materials in the form of liquids and solids. These materials may be solids, liquids or pastes, aqueous or organic, acidic or alkaline, e.g., detergent solutions, latices, foods or condiments, fine chemicals, etc., which may be poisonous. Two and one-half, five- and six-gallon sizes are most common. Because of inertness and toughness, plastics such as high density polyethylene or other inert moldable thermoplastic resins are preferred materials. The containers are filled with the contents, capped, perhaps stored, and shipped. After they are transported to the user, he may also store them. In storage, these containers are stacked one upon the other. After being opened, they may be reopened and closed as the contents are used. There are two common types of container constructions: the wide mouth or open-head pail and the closed mouth or tight-head pail. This invention relates to constructions for open-head pails so that they may have the structural characteristics associated with tight-head pails yet retain the wide mouth access of the open-head pails and yet remain child-proof.